The iron aluminum system forms a series of solid solutions from 0 to 52 atomic percent aluminum. At room temperature, alloys with less than 18.5 atomic percent (about 10 weight percent) aluminum are body-centered cubic solid solutions with a disordered structure. However, alloys with 18.5 to 35 atomic percent (about 10 to 18 weight percent) aluminum form a DO3 ordered structure, and alloys with greater than about 35 atomic percent (greater than about 18 weight percent) aluminum form the cubic B2 ordered structure.
Intermetallic iron aluminide alloys are of commercial interest because of their high tensile strength, low density, and excellent resistance at high temperatures to wear, corrosion and oxidation. According to commonly assigned Published U.S. Application No. 2002/0014453, nanoscale iron aluminides are also attractive as filtration materials, for example, for the selective abatement of 1,3-butadiene. However, as disclosed by Haber et al. in Advanced Materials, 1996, 8, No. 2 (pp. 163-166) and in Chem. Mater., 2000, 12 (pp. 973-982), commercial application of aluminides has been limited because coarse-grained aluminides are too brittle for many applications. As disclosed by Varin et al., in Intermetallics, 7 1999, (p. 917), particle size refinement, particularly to nanoscale (below 1 micron) dimensions, has been predicted to improve physical properties of iron aluminide intermetallic alloys.
As disclosed by Haber et al. in J. Aerosol Sci., Vol 29, No 5/6 (1998) (pp. 637-645), nanoscale particles have been made from metals, alloys, intermetallics and ceramics. U.S. Pat. Nos. 5,580,655; 5,695,617; 5,770,022; 5,851,507; 5,879,715; 5,891,548; 5,962,132; 6,262,129 and 6,368,406, the disclosures of which are all hereby incorporated by reference, relate to the formation of nanoscale particles using a variety of techniques including chemical synthesis, gas-phase synthesis, deposition by ionized cluster beams, high speed milling and sol-gel routes. These methods suffer from numerous drawbacks, however, including agglomeration, impurities or broad particle size distribution. In J. Mater. Res. Vol. 11, No. 2 (1996) (pp. 439-448 and 449-457) Suryanarayana et al. disclose the formation of nanocrystalline copper powder via the reduction of CuCl in NaBH4.
The most common method reported in the literature for the synthesis of intermetallic nanoparticles is mechanical ball milling. (See, for example, Jartych E., et al., J. Phys. Condens. Matter, 10:4929 (1998); Jartych E., et al., Nanostructured Materials, 12:927 (1999); and Amilis, X., et al., Nanostructured Materials 12:801 (1999)). Commonly assigned U.S. Pat. No. 6,368,406 discloses preparation of nanoscale FeAl by laser vaporization.
Despite the developments to date, there is interest in improved and more efficient methods of making aluminide materials and/or materials effective in reducing the amount of various constituents such as 1,3-butadiene in the mainstream smoke of a cigarette during smoking. Preferably, such methods and compositions should not involve expensive or time consuming manufacturing and/or processing steps.
Disclosed is a simple, novel and high yield approach for synthesizing iron aluminide and/or iron aluminum carbide nanoparticles via the chemical reduction of iron salts with lithium aluminum hydride. The chemical reduction technique provides several advantages including the capacity to generate large quantities of nanoscale particles.